The present invention relates to an optical signal processing device. In particular, the present invention relates to an optical hold unit that provides time delayed samples of an optical input signal on one or more optical output lines.
Optical systems are capable of manipulating and processing optical signals that, by their very nature, are extraordinarily fast. As an example, commonly available lasers exist that produce optical output pulses less than 0.5 ps (0.5.times.10.sup.-12 s) in duration at a repetition rate of more than 10 GHz (10.times.10.sup.9 Hz). Optical pulses typically propagate (using optical fiber, for example) at nearly the speed of light between optical processing elements.
The processing speeds achieved by optical processing elements far outstrip the processing speeds achieved by conventional electronic processing elements. However, electronic processing elements implement an incredible variety of signal manipulation and processing functions, most of which are not available as an equivalent optical processing element. One example is the ordinary microprocessor. A microprocessor may be programmed to implement almost any function, but has no analog as an optical processing element, particularly when cost and availability considerations are taken into account. In most instances, therefore, optical processing elements must interface with electronic processing elements at some point in order to take advantage of the wide variety of functions available through electronic processing. The optical signals are converted to electrical signals at the interface between the optical processing elements and the electronic processing elements.
As one of many possible examples, electronic analog to digital (A/D) converters are very common and very useful building blocks in digital processing systems. Commonly available electronic A/D converters, however, are simply not fast enough to work with the high speed signals provided by optical processing elements. Thus, a mechanism is required for "slowing down" an optical signal to a speed appropriate for an electronic A/D converter (or other processing element) before the electronic A/D converter may be used. Such a mechanism is termed an "optical hold unit".
In the past, however, no optical hold units have been available. As a result, optical processing elements were either not used in conjunction with electronic processing elements, or the optical processing elements are underutilized by carrying slower signals (in terms of pulse width and frequency, for example) on which electronic processing elements could operate.
A need has long existed in the industry for an optical hold unit that may interface with electronic processing elements.